1. Field of the Invention
The present invention relates to power windows designed to be used in vehicles such as automobiles for opening and closing windowpanes by means of driving sources such as motors or the like, and more particularly to a safety device for safely controlling the operation of the windowpanes by detecting a state in which, for example, the hand or head is caught between the windowpane and the window sash.
2. Description of the Related Art
In general, since a power window uses a motor or the like for opening and closing a windowpane of an automotive vehicle, there exists a risk of the hand or head of a passenger of the vehicle being caught between the windowpane and an associated window sash. Conventionally, there has been proposed a safety device for preventing an accident by detecting a state in which a foreign object is caught between a windowpane and a window sash of an automotive vehicle and stopping the closing or opening operation of the windowpane when such a state is detected. In a power window safety device like this, for example, a pulse signal oscillator comprising hole elements is mounted on a motor for driving the windowpane, and the absolute and relative speeds of the windowpane when it is closed and the direction in which the windowpane is operated are detected by a detecting means based on a pulse signal from the pulse signal oscillator. In addition, a safety control area is determined where a safety operation is to be carried out to deal with catching of a foreign object and thereafter, catching of a foreign object is detected based on a change in detected output of at least one of the absolute and relative speeds while the windowpane is being closed. Then, when a foreign object is detected as being caught, a safety control is effected in which the windowpane is forcibly operated in the opening direction, so that the foreign object is released from the state in which it is caught between the windowpane and the window sash.
In the safety control area determination technology described above, since there may occur a risk of erroneous determination of the safety control area due to an error in counting the pulse signal, a windowpane position detecting mechanism such as a limit switch is provided in the vicinity of an upper end of the windowpane for detecting a fully closed position of the windowpane with high accuracy, whereafter a safety control area is set. However, providing such a windowpane position detecting mechanism requires mounting position adjusting work in the assembly process in the assembly plant and involves complexity in assembly of vehicles. To omit such complex assembling work, the provision of an automatic position adjusting mechanism was conceived as described in JP-A-8-3-3113, but it led to the complex construction of the power window and has been a cause of higher production costs.
To cope with this, the position of the windowpane which is being operated to open or close is obtained by a position sensor and the opening or closing state of the windowpane is detected by an output from the position sensor. In this case, with a potentiosensor being disposed along a rail on which a windowpane is operated to open and close, since the resistance value of the potentiosensor changes in response to the position of the opening or closing windowpane, the opening or closing state of the windowpane is detected. However, in order to make this possible, a potentiosensor is required which is long enough to cover the whole opening and closing strokes of the windowpane, and providing such a long potentiosensor makes the vehicle window construction complex and the problem of higher production cost cannot be solved.
With a view to solving those problems, the applicant of this application for patent proposes in Japanese Patent Application No. 9-219395 a safety device for a power window comprising a position sensor for detecting the rotational angular position of a driving motor for operating a windowpane of a vehicle to open and close, means for detecting the position of the windowpane being operated to open or close based on an output from the position sensor and means for safely controlling the catching of a foreign object in the window. According to this safety device, not only can the whole opening and closing strokes of the windowpane be detected by the position sensor so as to detect catching of a foreign object in the window for safely controlling the occurrence thereof but also the simplification of the circuit which has been required for the safety device can be realized through the miniaturization of the position sensor. However, in this proposed safety device, of one rotation of the driving motor, an area up to a rotational angle of 330 degrees is used for detection of voltage changes from 0 to 5V corresponding to changes in rotational angle within the area. In recent years, however, more accurate safety control has been demanded and this demands in turn more accurate detection.
Thus, an object of the present invention is to improve further the safety device previously proposed to thereby provide a safety device for a power window which can perform safety control with higher accuracy by improving the detection accuracy and detection resolution of the detection by the position sensor of the position of a windowpane which is being operated to open or close.
The present invention provides a safety device for power windows in which a windowpane of a vehicle is operated to be opened and closed by a driving motor, and in which the position of the windowpane being operated to open or close is detected so as to safely control catching of a foreign object in a window, comprising a position sensor for detecting a rotational angular position of the driving motor, a position detecting means for detecting the position of the windowpane being operated to open or close based on an output from the position sensor, and a safety control means for safely controlling catching of a foreign object in a window based on the position detecting means, wherein the position sensor is constructed as a potentiosensor which has a resistance track comprising a circular electric resistor pattern and conductive brushes operable so as to slidingly rotate on the resistance track as the driving motor is driven, the resistance track being provided with electrodes at two diametrically opposed points on the circumference of the resistance track, and which is adapted to output from the conductive brushes resistance values resulting from division of a resistance value between the electrodes. For example, the potentiosensor is constructed such that a higher electric potential is supplied to one of the electrodes of the resistance track, while a lower electric potential is supplied to the other electrode and that the conductive brushes output potentials resulting from division of the higher electric potential and the lower electric potential, respectively. In addition, the conductive brushes comprise two conductive brushes which are deviated 90 degrees in a rotational direction thereof, and signals having different phases are outputted from the respective conductive brushes in correspondence with the rotational driving of the driving motor.
In the present invention, as a sensor for detecting the position of the windowpane which is being operated to open or close, the position sensor is provided for detecting the rotational angular position of the driving motor for opening and closing the windowpane, whereby the whole stroke of the windowpane from the fully closed position to the fully opened position is detected only through signals from the driving motor. This allows the miniaturization of the construction of the safety device and simplification of the circuit thereof, and equipment is thereby realized which is suitable for application to automotive vehicles. In addition, used as the sensor is a position sensor that has a circular resistance track and which is constructed so as to output resistance values resulting from the division of the resistance value between the terminals provided at the two diametrically opposed points of the circular resistance track, whereby the ratio of change in output from the position sensor relative to change in position of the windowpane is made larger to thereby enable highly accurate detection of the position of the windowpane, and there exists no state in which the output from the position sensor is made impossible depending on the rotational position of the driving motor to thereby stabilize the output property of the position sensor, enabling highly reliable detection of the windowpane position by the position sensor. Thus, according to the present invention, it is possible to construct a power window apparatus which can realize a more appropriate safety control.